A Melting Fossil traces how, since the nineteenth century, naturalists and scientists have used ice as a natural chronometer to understand the deep past and future of the Earth. Using archival sources that span two centuries and three continents, this project argues that through ice, Earth scientists have refashioned their conceptualization of deep time from something slow, lumbering, and uniform to something much more capricious—a shift that has profoundly shaped social understandings of environmental change. By tracing how scientific assertions about temporality have materialized, and how this materialization determines (and limits) cultural notions of and political actions on the past and future of the planet, A Melting Fossil reveals how deep time has expanded beyond the purview of the Earth sciences to form an epistemological frame for human-environment relationships.